Modular seat cushion with interlocking human support and base portions and method of creating and using a seat cushion

ABSTRACT

A modular seat cushion includes a human interface portion and a base portion which are combined and interlocked or interconnected together. The human interface portion has an upper support contour for supporting the user, and the base portion has a contact configuration for contacting a variety of different types of seat support structures. By selecting among human interface portions that have different sizes and shapes of support contours and by selecting among base portions that have a contact configuration appropriate for the seat support structure, a seat cushion is obtained which accommodates both the user and the type of seat support structure with which it is used. The ability to combine the human interface and base portions is particularly useful for wheelchairs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This invention is related to other inventions made by at least one ofthe inventors herein for Individually-Contoured Seat Cushion and ShapeCapturing and Fabricating Method for Seat Cushion described in U.S.patent application Ser. No. [249.301], and for Contoured Seat Cushionand Method for Offloading Pressure from Skeletal Bone Prominences andEncouraging Proper Postural Alignment described in U.S. patentapplication Ser. No. [249.303], and for Apparatus and Method forEvaluating Clearance from a Contoured Seat Cushion described in U.S.patent application Ser. No. [249.304], all of which are filedconcurrently herewith and all of which are assigned to the assignee ofthe present invention. The subject matter of these concurrently-filedapplications is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to seat cushions, and more particularly, to a newand improved modular seat cushion formed by a human support portion andan interlocking base portion. The human support portion providesindividualized support for the user, and the base portion fits with, isaccepted by, or becomes part of a seat support structure. By forming theseat cushion in this modular form, improved support, utility and comfortis available to the user for a relatively modest cost. The presentinvention is particularly useful to create seat cushions forwheelchairs, although the broader aspects of the invention are notlimited specifically to such use.

BACKGROUND OF THE INVENTION

A wheelchair seat cushion must perform a number of important functions.The seat cushion should be comfortable and capable of providing propersupport for optimal posture and posture control for a considerablelength of time. The seat cushion should also assist, or at least notmaterially hinder, the user in maneuvering the wheelchair, permit auseful range of motion from the pelvis and upper torso of the person,and create stability and security for the person within the wheelchair.Perhaps most importantly, the seat cushion should help prevent andreduce the incidence of pressure ulcers created by prolonged sitting onthe cushion without adequate pressure relief. Pressure ulcers can becomea very serious health problem for individuals who must remain constantlyin contact with the support cushion, and it is important to avoid suchpressure ulcers.

Wheelchair users like everyone are of substantially different sizes,weights and shapes. Many wheelchair users have physical disabilities andassociated posture and postural control impairments such as thosetypically caused by congenital disorders. Other wheelchair users, suchas those who have been disabled by acquired or traumatic injuries, mayhave a more typical size and shape. In all of these cases, the supportcontour of the wheelchair seat cushion must safely support the anatomyof the user, whether the anatomy is abnormal or more typical. Wheelchairseat cushions must fit and perform properly to prevent further physicalimpairment and pressure ulcers. The cushion must also enhance thefunctional capabilities of the user by supporting independence inactivities of daily living. There are a number of different theories orapproaches for configuring the support contour of a wheelchair seatcushion to avoid pressure ulcers and to provide adequate posturalalignment.

A variety of different wheelchairs are also available. Many of thesedifferent wheelchairs have physically different constructions andshapes. The seat support structures of these wheelchairs may varysubstantially. One type of wheelchair seat support structure is a slingseat. A sling seat is made of fabric material that is suspended betweentwo frame rails of the wheelchair. The wheelchair cushion is placed ontop of the sling seat. A sling seat will bend or sag downward due to theweight of the user and its flexible nature. A platform seat is anothertype of wheelchair seat structure. A platform seat is generally a flatand rigid structure which is connected on top of the wheelchair framerails. The cushion is placed on top of the platform seat. A drop seat issimilar to a platform seat, except that the platform is located andsuspended below the frame rails. A drop seat positions the person closerto the ground and creates a slightly lower center of gravity for thewheelchair and user. Shell seats and pan seats may also be used aswheelchair seat support structures. A shell seat is a single chair-likeshape having a seat bottom and a seat back. In general, a shell seat isused when the wheelchair user is incapable of supporting himself orherself. A pan seat is similar to the seat bottom of a shell seat or toa curved platform seat. A pan seat may be used under specialcircumstances where other types and forms of wheelchair seat supportsare not appropriate or preferred.

To provide the best wheelchair cushion for a user, the cushion must bedesigned to accommodate and support the anatomy and functionalpreferences of the user, as well as the type of seat support structurepreferred by the user. In general, the predominant previous approach toaccommodating these requirements has involved using generic wheelchaircushions which have some capability of adapting to the anatomical shapeof the user and then rigging an attachment of the cushion to thewheelchair. The ability of the cushion to adapt to different users isoften accomplished by soft, flowable or adaptable cushion material whichredistributes under the weight of the user to accommodate the differentanatomical shapes of different users. The attachment of the cushion tothe wheelchair usually requires additional use of auxiliary attachmentdevices and hardware which must oftentimes be specifically fabricatedfor that purpose.

Generic seat cushions may not be comfortable or offer the best fit for aparticular user. The size, posture and anatomical characteristics of anindividual may influence the comfort and fit of the seat cushion.Certain of these anatomical areas have a prominent skeletal bonestructure. Excessive pressure in the areas of prominent bone structureincreases the risk of pressure ulcers which can have very seriousmedical consequences. The problems of existing seat cushions arediscussed more completely in the concurrently filed U.S. patentapplication Ser. No. [249.303] referenced above.

Having a custom wheelchair cushion built to accommodate the anatomy andpreferences of a specific individual is an option which overcomes thedisadvantages associated with generic wheelchair cushions. There are anumber of very sophisticated methods and devices available to createcustom wheelchair cushions, but the ability to capture and use theanatomical shape of the user when creating the cushion is veryimportant, as discussed in U.S. patent application Ser. No. [249.301]referenced above. Furthermore, even if the support contour of the customcushion is initially satisfactory, that support contour may ultimatelyprove to be inappropriate or uncomfortable after the cushion has beenused for some period of time. Tissue changes influenced by continuallysitting on the cushion over some period of time may change the optimalsupport and comfort characteristics. It is also typical that tissue mayatrophy over time, particularly for first-time wheelchair users, furthercompromising cushion fit.

Another problem with custom wheelchair cushions is that the user is notable to test or try the cushion before it is fabricated. The user cannotevaluate the support from the cushion and cannot evaluate the seatingposition in the wheelchair. If the cushion positions the user too farforward or rearward, or too low or high, the ability of the user to turnthe drive wheels and maneuver the wheelchair is adversely affected.Turning the drive wheels also causes the pelvis and torso of the user torock forward and backward. This movement is normal and desirable, butmay increase the shear forces experienced at the seat interface therebyfurther elevating risk for skin breakdown and pressure ulcers.

The cost of a custom wheelchair or cushion can also be a substantialdetriment. Creating a custom wheelchair cushion may cost in theneighborhood of approximately $3000 or more. Custom cushions areexpensive because of the time consumed to make them and the cost of therelatively sophisticated equipment necessary to simulate individualanatomical contours of the user into a support contour of the customcushion.

Connecting and adapting any of these seat cushions to a wheelchair seatsupport structure is not an insignificant matter. Each different type ofwheelchair seat support structures usually requires a different type ofattachment arrangement. Standard attachment hardware for each differenttype of wheelchair seat support structure is not readily available.Consequently, auxiliary attachment hardware and devices must beindividually ordered or fabricated. Varying degrees of functionality andsuccess in attaching the seat cushion are common results in suchcircumstances. In general, the auxiliary attachment hardware adds weightto the wheelchair, making maneuverability of the wheelchair moredifficult or strenuous.

Many of the same considerations also apply with varying levels ofcriticality to other uses of seat cushions. For example, seat cushionsused in office environments are required to support the user in acomfortable manner which encourages proper posture and without creatingrisks of medical problems, for example inducing blood circulatoryproblems.

SUMMARY OF THE INVENTION

The present invention obtains the benefits of a custom seat cushion at amodest fraction of the typical cost for a custom seat cushion, whilesimultaneously facilitating attachment and support of the cushion to aseat support structure. To do so, the seat cushion is formed in twoportions. An upper human interface portion defines a support contour forthe user's anatomy while seated. A lower base portion defines a contactconfiguration which complements and is supported against a seat supportstructure. The human interface portion and the base support portion areinterconnected to complete the cushion.

The human interface portion is preferably formed with different supportcontours, thereby allowing human interface portion to be selected foruse which best accommodates the anatomy of the user. A relatively smallnumber of human interface portions, for example three, with differentsized and shaped support contours will accommodate a significantpopulation of users having normal anatomies. For those wheelchair userswho have an abnormal anatomy, the human interface portion is formed witha specific custom support contour to accommodate the peculiarities ofthe abnormal anatomy. The lower base portion accommodates the user'spreference for a type of seat support structure. Examples of wheelchairseat support structures include a platform seat, a sling seat, a droppedplatform seat, a pan seat and a shell seat. A number of different baseportions, each with a different contact configuration, allows thecushion to be used with any of the typical seat support structureswithout the need for cost of additional parts and accessories.Interconnecting the upper human interface portion with the lower baseportion allows the seat cushion to complement the anatomy of the userand the seat support structure without the need for and cost ofadditional parts and accessories.

The user can test or demonstrate the modular cushion to confirm that itprovides the desired comfort and maneuverability prior to accepting thecompleted cushion. To the extent that testing demonstrates that changesare required, those changes may be achieved by interchanging one or bothof the upper human interface and lower base portions. Future adjustmentsin the seat cushion can be accomplished by changing one or both of theupper human interface portion or the lower base portion to accommodatechanges in the user's needs or preference for seat support structures,respectively. Because most of the human interface portions and the baseportions are standard configurations, they can be mass produced for muchless cost than if the entire cushion was custom made. In most cases,there is no need for a custom cushion, because a cushion can beassembled from standard variations of human interface portions.Furthermore, assembling the cushion from the standard human interfaceand base portions will make the completed cushion available for use on amore rapid basis.

One aspect of the invention involves a modular seat cushion whichincludes the human interface portion and the base portion. The humaninterface portion has an upper surface area defining a support contourfor supporting an anatomical portion of the person while seated on thecushion. The human interface portion also has a lower surface areadefining a first one of two complementary portions of an interlockingstructure. The base portion has an upper surface area defining a secondcomplementary portion of the interlocking structure and also has a lowersurface area defining a contact configuration. The first and secondcomplementary portions of the interlocking structure interconnect withone another when the lower surface area of the human interface portioncontacts the upper surface area of the base portion. The contactconfiguration has a predetermined shape which complements at least aportion of the seat support structure.

Another aspect of the invention involves a method of creating a modularseat cushion. The method comprises selecting a human interface portionfrom among a plurality of different human interface portions which eachhave a different support contour, selecting a base portion from among aplurality of different base portions which each have a different contactconfiguration for a seat support structure, and combining the selectedhuman interface portion with the selected base portion to position thesupport contour in complementary contact with the anatomical portion ofthe person and to position the contact configuration in complementarycontact with the seat support structure.

Another aspect of the invention involves supporting a person on a seatsupport structure. This method comprises selecting the human interfaceportion with the desired support contour, selecting the base portionwith the desired contact configuration, combining the selected humaninterface portion with the selected base portion, positioning thecontact configuration into complementary contact with the seat supportstructure, and seating the person on the cushion with the anatomicalportion of the person in contact with the support contour of the humaninterface portion.

Another aspect of the invention involves including in the seat supportstructure a portion which has essentially the same shape characteristicsas the second complementary portion of the interlocking structure of thebase portion, and then interfitting the selected human interface portionwith the seat support structure.

Another aspect of the invention involves attaching a human interfaceportion of a seat cushion to a seat support structure of a wheelchair.The human interface portion includes a support contour for supporting ananatomical portion of a person on the seat cushion, and the seat supportstructure has a predetermined configuration for supporting the seatcushion and the person seated on the cushion. The method involvesinterposing a base portion between the human interface portion and theseat support structure of the wheelchair, interconnecting the baseportion and the human interface portion, and contacting the base portionin a complementary manner with the predetermined configuration of theseat support structure.

The present invention is particularly applicable to seat cushions forwheelchairs. Other preferable features of the invention involve formingthe human interface and base portions from flexible support materialssuch as a resilient breathable plastic foam material, forming thecomplementary interlocking portions of the interlocking structure fromthe flexible support material, and employing consistent complementaryportions of the interlocking structure so that the different humaninterface portions and base portions will interfit and connect together.

A more complete appreciation of the scope of the present invention andthe manner in which it achieves the above-noted and other improvementscan be obtained by reference to the following detailed description ofpresently preferred embodiments taken in connection with theaccompanying drawings, which are briefly summarized below, and byreference to the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded and perspective view of a wheelchair and a modularseat cushion which incorporates the present invention, with a portion ofthe seat cushion shown broken away to show the internal structure of theseat cushion.

FIG. 2 is an enlarged and exploded downward-looking perspective view ofthe top of a top human interface portion and the top of a bottom baseportion of the seat cushion shown in FIG. 1.

FIG. 3 is a upward-looking perspective view of the bottom of the tophuman interface portion and the bottom of the base portion shown in FIG.2.

FIG. 4 is a longitudinal and vertical cross-sectional view of the seatcushion shown in FIG. 1 taken substantially in the plane of line 4-4,with the human interface and bottom support portions shown in aninterconnected relationship.

FIG. 5 is an exploded front elevational view of a wheelchair having aplatform seat support structure, and a wheelchair seat support cushionformed by a combined human interface portion and a base portion, asshown in FIG. 1, in which the base portion has a contact configurationwhich complements the platform seat support structure.

FIG. 6 is an exploded front elevational view of a wheelchair having asling seat support structure, and a wheelchair seat cushion formed by acombined human interface portion and a base portion, similar to thatshown in FIG. 1, in which the base portion has a contact configurationwhich complements the sling seat support structure.

FIG. 7 is an exploded front elevational view of a wheelchair having adropped platform seat support structure, and a wheelchair seat cushionformed by a combined human interface portion and a base portion, similarto that shown in FIG. 1, in which the base portion has a contactconfiguration which complements the dropped platform seat supportstructure.

FIG. 8 is an exploded front elevational view of a wheelchair having apan seat support structure, and a wheelchair seat cushion formed by acombined human interface portion and a base portion, similar to thatshown in FIG. 1, in which the base portion has a contact configurationwhich complements the pan seat support structure.

FIG. 9 is an exploded front elevational view of a wheelchair havinganother pan seat support structure, different from that shown in FIG. 8,and a wheelchair seat cushion formed by a combined human interfaceportion and a base portion, similar to that shown in FIG. 1, in whichthe base portion is a part of the pan seat support structure.

FIG. 10 is an exploded front elevational view of a wheelchair having ashell seat support structure, and a wheelchair seat cushion formed by acombined human interface portion and a base portion, similar to thatshown in FIG. 1, in which the base portion is a part of the shell seatsupport structure.

FIG. 11 is chart illustrating the combination of different humaninterface portions and base portions of the seat cushion shown in FIGS.1-10 to accommodate the different types of the wheelchair seat supportstructures shown in FIGS. 5-10.

DETAILED DESCRIPTION

A modular wheelchair seat cushion 20 is used with a seat supportstructure 22 of a conventional wheelchair 24 as shown in FIG. 1. Oneembodiment of the seat cushion 20 comprises a human interface portion 26and a base portion 28 which fit together in an interlocking manner, asshown in FIGS. 1-4. Another embodiment of the seat cushion 20 interlocksthe human interface portion 26 with a complementary portion of a seatsupport structure, as shown in FIGS. 9 and 10. The human interfaceportion 26, and the base portion 28 (when used), are covered by aconventional covering 30 to complete the seat cushion 20.

An upward-facing support contour 32 is formed in the human interfaceportion 26 to support the user when the user sits on the cushion 20, asshown in FIGS. 1, 2 and 4. Different human interface portions 26 willeach have differently-shaped support contours 32 to accommodate thedifferent anatomies of different users, when the user sits on thesupport contour 32 of the cushion 20.

The base portion 28 includes a downward-facing contact configuration 34which interacts with a particular type of seat support structure 22.Examples of different types of wheelchair seat support structures 22 area platform seat 36, shown in FIGS. 1, 4 and 5; a sling seat 38, shown inFIG. 6; a dropped platform seat 40, shown in FIG. 7; a pan seat 42,shown in FIG. 8; another type of pan seat 44, shown in FIG. 9; and ashell seat 46, shown in FIG. 10. All of these wheelchair seat supportstructures 36-46 are typically connected to longitudinally extendingrails 48 of a frame 50 of the wheelchair 24.

The interaction of the contact configuration 34 of the base portion 28with the seat support structure 22 maintains the cushion 20 in place onthe wheelchair 24, in one embodiment of the invention. In the otherembodiment of the invention, the human interface portion 26 directlyinteracts and complements a particular type of seat support structure 22without the use of a separate base portion 28 of the cushion 20. In thissecond embodiment, the portion of the human interface portion 26 whichnormally interacts directly with the base portion 28 instead directlyinteracts with the seat support structure 22 to hold the human interfaceportion 26 in the seat support structure 22 without the need of aseparate base portion 28. The covering 30 typically extends only overthe human interface portion 26, in this second embodiment.

By employing a particular support contour 32 of the human interfaceportion 26 which comfortably fits and supports the anatomy of aparticular user, and by selecting a base portion 28 or human interfaceportion 26 which has a contact configuration that matches and conformswith the type of wheelchair seat support structure 22, a wheelchair seatcushion 20 is obtained which offers significant benefits for the user.The comfort and fit of the support contour 32 offers the capability forsignificant freedom from pressure ulcers. The cushion allows enhancedmaneuverability, stability and use of the wheelchair. These benefits areavailable from any wheelchair having any of the common and conventionalseat support structures 22. By mass producing different human interfaceportions 26 with different support contours 32 and by mass producingdifferent base portions 28 with different contact configurations 34, andby then combining the human interface portions 26 according to theanatomy of the user with the base portions 28 according to the differenttypes of wheelchair seat support structures 22, the resulting cushion 20can very closely simulate the benefits of a custom wheelchair cushion,but without the added cost of a custom wheelchair cushion. When a customcushion is required or desired by the user, only the support contour 32of the human interface portion 26 must be specially fabricated, and notthe entire cushion, since a standard base portion 28 can be used withthe specially fabricated human interface portion 26. Standard contactconfigurations 34 make retention on the wheelchair seat supportstructure relatively easy to accomplish without incurring the cost andeffort of modifying a cushion to accommodate a particular wheelchairsupport structure and without fabricating or using additional supportand retention hardware.

The human support contour 32 of the human interface portion 26 isillustrated in FIGS. 2 and 4. The support contour 32 may be shaped toaccommodate a normal human anatomy, with only the size and proportion ofthe support contour 32 adjusted to accommodate different sizes andshapes of users. The support contour 32 of the human interface portion26 may also be formed in a custom configuration to accommodate thespecific anatomical uniqueness of a user who may not fit or prefer astandard variation support control 32.

Preferably, the shape and proportion of the standard variations in thesupport contour 32 will be as described in U.S. patent application Ser.No. [249.303], referenced above. The support contour described in thisU.S. patent application has considerable advantages and improvements inavoiding pressure ulcers while providing improved postural alignment forthe user. Adjusting the size and proportion of this standard supportcontour 32 accommodates different sizes and shapes of the normalanatomy. For example, one standard variation of the support contour 32is intended to primarily accommodate the wider spread and shallowerslope of the ischial tuberosities of the female skeletal bone structure.Another standard variation of the support contour 32 is intended toaccommodate the narrower and steeper slope of the ischial tuberositiesof the male skeletal bone structure. Another standard variation of thesupport contour 32 is not gender-specific, but has a deeper and steeperprofile. This deeper and steeper support contour 32 may provide betterprotection for individuals with soft tissue atrophy. However, regardlessof sex or degree of tissue atrophy, any user may prefer any one of thesedifferent standard variations of support contours, depending on personalcomfort, support and preference.

In general, a variety of different support contours and theories forsupporting wheelchair users are known and available, in addition to thesubject matter described in U.S. application Ser. No. [249.303]. Anytype of support theory can be implemented in the support contour 32 ofthe human interface portion 26, in accordance with the presentinvention.

In those cases where an individualized or custom support contour 32 isdesired, that custom support contour 32 must be derived and made fromthe particular anatomical characteristics of the individual user. Anumber of known techniques are available to create custom wheelchaircushions, and those known techniques may be applied to create thesupport contour 32 and the human interface portion 26 in accordance withthe invention. One particularly useful type of technique for creating aseat cushion is described in U.S. patent application Ser. No. [249.301],referenced above. That technique is applicable to fabricating both thehuman interface portion 26 and the base portion 28.

The human interface portion 26 and the base portion 28 areinterconnected mated or interfitted together by an interlockingstructure 52. One example of an interlocking structure 52 is shown inFIGS. 2-4. The interlocking structure 52 includes a protrusion 54 whichextends downward (as shown) from a lower surface 56 of the humaninterface portion 26. The protrusion 54 fits within a complementaryshaped recess 58 formed into the base portion 28 from an upper surface60 of the base portion. The lower surface 56 of the human interfaceportion 26 and the upper surface 60 of the base portion 28 are shaped ina mutually complementary manner, as shown in FIG. 4. The surfaces 56 and60 contact one another when the protrusion 54 fits within the recess 58.The complementary interfitting relationship of the protrusion 54 withinthe recess 58, and the complementary interfacing contact of the surfaces56 and 60, interlock the human interface portion 26 with the baseportion 28, as shown in FIG. 4. When interlocked in this manner, theportions 26 and 28 will not readily separate, particularly when coveredor encased with a relatively tight covering 30 (FIG. 1) or when heldtogether with adhesive. Although not shown, other indexingconfigurations or shapes may be formed on the surfaces 56 and 60 tointerfit with one another, to supplement and/or substitute for theinterfitting relationship of the protrusion 54 and the recess 58.

The interlocking structure 52 is of a consistent configuration among allof the different types of human interface portions 26 and base supportportions 28. The protrusion 54 and the lower surface 56 of the humaninterface portion 26 have consistent shapes and dimensions on all of thedifferent types of human interface portions 26. Similarly, the recess 58and the upper surface 60 of the base portion 28 have consistent shapesand dimensions on all of the base portions 28. Consequently, any of thedifferent types of human interface portions 26 will interconnect, mateand interfit with any of the different types of the base portions 26.

Depending upon the thickness of the base portion 28, the recess 58 mayextend completely through the base portion 28, in which case the recess58 constitutes a hole completely through the base portion 28 as shown inFIGS. 2 and 4. In this embodiment when the portions 26 and 28 areinterlocked and placed on the seat support structure 22 of thewheelchair, the protrusion 54 contacts and rests against the seatsupport structure 22, separated only by the thickness of the covering30. Using a hole as the recess 58 in the base portion 28 configurationallows the human interface portion 26 to have a relatively deep supportcontour 32 while still interfitting with the base support portion 28,and to maintain as low of a center of gravity of the user as possible.

The contact configuration 34 of the base portion 28 includes a lowersurface 62 (FIGS. 3 and 4) which substantially fully contacts andcomplements one type of wheelchair seat support structure 22. The commonand prevalently used types of wheelchair seat support structures 22 areillustrated in FIGS. 5-10.

A typical platform wheelchair seat support structure 36 is shown inFIGS. 1, 4 and 5. The platform seat support structure 36 is formed by arigid, generally planar sheet member 64 which extends between the rails48 of the wheelchair frame 50. For example, the sheet member 64 may beformed from plywood, metal, or composite material. The sheet member 64is attached to the rails 48 by conventional fasteners (not shown). Theupper surface of the sheet member 64 is planar. To fully contact andcomplement the upper planar surface of the sheet member 64, the contactconfiguration 34 of the base portion 28 is made as a planar surface 62a, shown in FIG. 5. When a base portion 28 with a lower planar surface62 a rests on the upper planar surface of the sheet member 64, the shapeof the recess 58 and upper surface 60 (FIGS. 2 and 4) are not distortedfrom their intended shapes, thereby allowing the protrusion 54 and thelower surface 56 to fit within and contact the recess 58 and the uppersurface 60, respectively, to interlock the human interface portion 26and the base portion 28.

A typical sling seat 38 is another type of wheelchair seat supportstructure 22, shown in FIG. 6. The sling seat 38 is formed by strong andflexible material 66, such as durable fabric, which is connected orsuspended in a sling-like manner between the rails 48. The material 66is connected to each of the rails 48 by looping each end of the material66 around a longitudinally-extending support bar (not shown) and thenconnecting each end of the material 66 to the middle portion of thematerial 66 with a conventional hook and loop fastener. Thelongitudinally extending support bar (not shown) is then attached to therails 48 with conventional fasteners (not shown).

In general, the sling seat 38 will sag or curve downward between therails 28 as generally shown in FIG. 6. Consequently, in order to fullycontact and complement the curved shape of the material 66 forming thesling seat 38, the contact configuration 34 of the base portion 28 isformed with a complementary downwardly-curved convex lower surface 62bshown in FIG. 6. When a base portion 28 with the downwardly-curved lowersurface 62 b rests on the downwardly curved material 66 of the slingseat 38, the shape of the recess 58 and upper surface 60 (FIGS. 2 and 4)are not distorted from their intended shapes, thereby allowing theprotrusion 54 and the lower surface 56 to interfit with the recess 58and the upper surface 60, respectively, and thereby interconnect thehuman interface portion 26 and the base portion 28.

A typical dropped platform wheelchair seat support structure 40 is shownin FIG. 7. The dropped platform seat 40 is similar to the platform seat36 (FIG. 5), except that the dropped platform seat 40 is suspendedbeneath and between the rails 48. The dropped platform seat 40 is formedby a rigid, generally planar sheet member 70 which is suspended from therails 48 by suspension brackets 72. For example, the sheet member 70 maybe formed from plywood, metal or composite material. Conventionalfasteners (not shown) connect the suspension brackets 72 to the sheetmember 70 and connect suspension brackets 72 to the rails 48. The uppersurface of the sheet member 70 is planar, and the upper surface islocated at a position lower than the rails 48 of the wheelchair frame 50(FIG. 1).

To fully contact and complement the upper planar surface of the sheetmember 70, and to extend over the top of the rails 48, the contactconfiguration 34 of the base portion 28 is formed as a lower planarsurface 62 c with longitudinal edge recesses 74 extending along eachtransverse side of the base portion 28. The recesses 74 fit around thesuspension brackets 72 and the rails 48, thereby allowing a portion ofthe base support 28 to extend over and around the rails 48. When a baseportion 28 with a planar lower surface 62 c and recesses 74 rests on theplanar surface of the sheet member 70 and fits around the suspensionbrackets 72 and the rails 48, the shape of the recess 58 and uppersurface 60 (FIGS. 2 and 4) are not distorted from their intended shapes,thereby allowing the protrusion 54 and the lower surface 56 to interfitwith the recess 58 and the upper surface 60, respectively, and therebyinterconnect the human interface portion 26 and the base portion 28.

A pan seat 42, shown in FIG. 8, is another type of wheelchair seatsupport structure 22. The pan seat support structure 42 may take avariety of different configurations. In general, the pan seat 42 willalways include a bottom wall 76 which extends between the rails 48. Thebottom wall 76 may be generally planar, as shown in FIG. 8, or thebottom wall 76 may curve slightly downward similar to the curve of thesling seat 38 (FIG. 6). The pan seat 42 may also include edges 78 whichextend upward from the periphery of the bottom wall 76. The edges 78will not extend along a front edge of the bottom wall 76 where the legsof the user will bend when the user is seated in the pan seat 42. Thepan seat 42 is preferably formed of rigid material, for examplelightweight composite material. The pan seat 42 is attached to the rails48 by conventional fasteners (not shown) or rests on the sling seat 38(FIG. 6) with hook and loop attachment. In a sense, the pan seat 42 issimilar to the platform seat 36 (FIG. 5), except that it may alsoinclude the edges 78 and may have a curved bottom wall 76.

The contact configuration 34 of the base portion 28 is formed as asurface 62d which has been curved and shaped in a manner to fullycontact and complement any curvature and shape of the bottom wall 76.The base portion 28 should also be shaped to fit within the edges 78.When a base portion 28 with an appropriately-shaped contact surface 62 drests on the bottom wall 76 and within the edges 78, the recess 58 andupper surface 60 (FIGS. 2 and 4) are not distorted from their intendedshapes, thereby allowing the protrusion 54 and the lower surface 56 tointerfit with the recess 58 and the upper surface 60, respectively, andinterconnect the human interface portion 26 and the base portion 28.

Another type of pan seat wheelchair support structure 44 is shown inFIG. 9. The pan seat 44 is similar to the pan seat 42 (FIG. 8) butincludes a receptacle 82 formed in a bottom wall 84 of the pan seat 44.The receptacle 82 has the shape and configuration of the recess 58 ofthe base portion 28 (FIGS. 2 and 4). In addition, the upper surface ofthe bottom wall 84 which surrounds the receptacle 82 has the shape andconfiguration of the upper surface 60 of the base portion 28 (FIGS. 2and 4). Shaped in this manner, the receptacle 82 and the upper surfaceof the bottom wall 84 are capable of interconnecting in a complementarymanner with the protrusion 54 and the lower surface 56 of the humaninterface portion 26 (FIGS. 3 and 4).

The human interface portion 26 is interconnected directly with the panseat 44 as a result of the protrusion 54 of the human interface portion26 extending into the receptacle 82 and the lower surface 56 of thehuman interface portion 26 (FIGS. 2-4) resting on the bottom wall 84 ofthe pan seat 44. Use of the base portion 28 (FIGS. 1-4) is unnecessarybecause a portion of the seat pan 44 becomes the base portion 26.Interconnecting the complementary portions of the human interfaceportion 26 and the seat pan 44 interlocks the human interface portion 28and the pan seat 44.

The pan seat 44 is attached to the rails 48 with fasteners (not shown).The pan seat 44 may also include edges 78 which extend upward from theperiphery of the bottom wall 84, except that the edges 78 will notextend along a front edge of the bottom wall 84 where the legs of theuser will bend when the user is seated in the pan seat 44. In theembodiment shown in FIG. 9, only the human interface portion 26 isenclosed within a covering 30.

A complete shell seat 46 is another type of wheelchair seat supportstructure 22, as shown in FIG. 10. The shell seat support structure 46includes a bottom wall 86 which may be similar in shape andconfiguration to one of the bottom walls 76 and 84 of the pan seats 42and 44 (FIGS. 8 and 9), respectively. In addition, the shell seat 46includes a back wall 88 which extends vertically upward from the bottomwall 86 at a location to contact the back of the upper torso of thewheelchair user. The shell seat 46 may also include edges 78 whichextend longitudinally on opposite transverse sides of the bottom wall86, from the back wall 88 forward. Preferably, the entire shell seat 46is formed as a rigid integral structure of lightweight compositematerial. The shell seat rests on a sling seat 66 of a typicalwheelchair and an anchoring strap 89 secures the seat to the wheelchair.

Depending upon the shape and configuration of the bottom wall 86, thecushion 20 used with the shell seat 46 may or may not include a baseportion 28 (FIGS. 1-4). If the bottom wall 86 has a configurationsimilar to the bottom wall 76 of the pan seat 42 shown in FIG. 8 but notshown in FIG. 10, the contact configuration 34 of the base portion 28will be formed as a lower surface 62 which has a shape which complementsthe bottom wall 86. If the bottom wall 86 has a configuration similar tothe bottom wall 84 of the pan seat 44 shown in FIG. 9 and also shown inFIG. 10, and thereby includes the receptacle 82, the base portion 28will not be part of the cushion 20. Instead, the human interface portion26 will interconnect directly with the bottom wall 86. Whether or not abase portion 28 is used, the human interface portion 26 will be retainedwithin the shell seat 46. Although not shown in FIG. 10, a cushion orother type of padding will typically be attached to the back wall 88 toprovide comfort, support and protection for the upper torso of the user.

The human interface portion 26 and the base portion 28 may be formed offlexible support material such as moldable plastic foam. Oneparticularly advantageous type of material from which to make the humaninterface portion 26 and the base portion 28 is plastic beads, asdescribed more completely in U.S. patent applications Ser. Nos. [249.301and 249.303]. The plastic bead material is fused together in such a waythat spaces exist between the individual fused beads. The spaces betweenthe individual fused beads make the portions 26 and 28 breathable in thesense that air will move through them, thereby providing ventilationthrough the cushion to the user. In addition, the base portion 28 may beformed somewhat more rigidly and having less flexibility than the humaninterface portion 26, to add structural stability to the cushion 20. Thehuman interface portion 26 may be somewhat more flexible to accommodateinteraction with the user's anatomy. The differences in flexibility andrigidity may be accommodated by using different sizes and resilienciesof plastic beads and different degrees of compaction of those plasticbeads when fusing them together, as described in U.S. patentapplications Ser. Nos. [249.301 and 249.303].

The human interface portion 26 and the base portion 28 may bepermanently connected or held together with an adhesive. However, due tothe interlocking structure 52 shown in FIGS. 2-4, the portions 26 and 28may also be held together by a closely-surrounding or encasing covering30. Holding the portions 26 and 28 together in a nonpermanent mannerallows each of the individual portions 26 and 28 to be changed asnecessary to accommodate changing needs of the user and changes inpreferences for seat support structures.

The covering 30 can be any type of impervious material, if a liquidresistant seat cushion 20 is required. However, to take advantage of thebreathable characteristics of the portions 26 and 28, the covering 30 ispreferably a fabric or some other type of material which allows air topass through it.

The chart shown in FIG. 11 illustrates the interchangeability of thehuman interface portions 26 and the base supports 28 with differentwheelchair seat support structures. The different types of humaninterface portions discussed above are generally represented by theleft-hand column in FIG. 11. These types of human interface portions 26each include a different variation of the support contour 32 (FIGS. 2and 4). Those standard variations are represented by a female variationsupport contour 90, a male variation support contour 92, and anon-gender-specific contour 94 which is intended to accommodate greaterdegrees of tissue atrophy. All of these support contours have beendiscussed generally above. The human interface portion 26 may also use acustom support contour 96 which is configured to interface specificallywith the anatomy of a particular individual, as also discussed above.The right hand column in FIG. 11 represents the different types ofconfigurations 34 of the base portions 28 which may be used toaccommodate the different types of common wheelchair seat supportstructures or which may be part of the wheelchair seat supportstructures. Those types of different seat support structures include theplatform seat 36 (FIGS. 1 and 5), the sling seat 38 (FIG. 6), thedropped platform seat 40 (FIG. 7), the pan seats 42 and 44 (FIGS. 8 and9) and the shell seat 46 (FIG. 10).

By using the human interface and base portions 26 and 28 in connectionwith any of the seat support structures 22 in the manner described, theresulting seat cushion 20 provides support for the wheelchair user whileoffering a high level of relative protection to the wheelchair useragainst pressure ulcers. Simultaneously, the needs and preferences ofthe user are accommodated with respect to a particular type of seatsupport structure on a particular type of wheelchair. These benefits areobtained without the need for additional hardware and attachmentaccessories that add to the cost of the cushion and the weight of thewheelchair. Moreover, the modularity and interfitting relationship ofthe seat cushion offers a relatively inexpensive and effective way toprovide a highly functional seat cushion which closely approximates thebenefits of a custom seat cushion. For those users who require or desirea custom seat cushion, the custom human interface portion may still beinterconnected with a standard base portion to obtain the benefits ofstandard base variations. A relatively few variations of human interfaceportions 26 and base portions 28, represented in FIG. 11, willaccommodate the substantial majority of the seat support structureswhich are commonly and prevalently available for use by wheelchairusers.

Most of the same improvements are applicable to use of the presentinvention for seat cushions in environments other than wheelchair seatcushions, for example chairs used in office environments. A desired typeof human interface portion 26 may be selected according to thepreferences of the user, and the type of base portion 28 is selectedaccording to the type of seating structure upon which the user prefersto connect the human interface portion 26. In this manner, the benefitsof the human interface portion for supporting the user are available ona variety of different types of seating devices and structures. Manyother advantages and improvements will be apparent upon comprehendingthe full significance of the present invention, not only for use withwheelchairs but for other applications as well.

Presently preferred embodiment of the invention and many of itsimprovements have been described with a degree of particularity. Thisdescription is of preferred examples of implementing the invention, andis not necessarily intended to limit the scope of the invention. Thescope of the invention is defined by the following claims.

1. A modular seat cushion for supporting a person against a seat supportstructure of a predetermined configuration, comprising: a humaninterface portion having an upper surface defining a support contour forsupporting an anatomical portion of the person while seated on thecushion and also having a lower surface defining a first one of twocomplementary portions of an interlocking structure; and a base portionhaving an upper surface defining a second one of the two complementaryportions of the interlocking structure and also having a lower surfacedefining a contact configuration for contacting the seat supportstructure, the second complementary portion interconnecting with thefirst complementary portion upon contacting the lower surface of thehuman interface portion with the upper surface of the base portion, thecontact configuration having a predetermined shape which complements atleast a portion of the predetermined configuration of the seat supportstructure which the contact configuration contacts.
 2. A modular seatcushion as defined in claim 1, wherein: the human interface portion andthe base portion are both formed of resilient synthetic plastic supportmaterial.
 3. A modular seat cushion as defined in claim 2, wherein: theresilient synthetic plastic support material is breathable.
 4. A modularseat cushion as defined in claim 1, wherein: the human interface andbase portions each comprise resilient plastic beads which have beenfused together.
 5. A modular seat cushion as defined in claim 4,wherein: the first and second complementary portions of the interlockingstructure are formed of flexible plastic beads which have been fusedtogether.
 6. A modular seat cushion as defined in claim 4, wherein: thehuman interface and base portions are formed substantially entirely ofthe fused together resilient plastic beads.
 7. A modular seat cushion asdefined in claim 2, wherein: the first and second complementary portionsof the interlocking structure are formed integrally with the humaninterface and base portions, respectively; and the first and secondcomplementary portions of the interlocking structure are formed of theresilient synthetic plastic support material from which the humaninterface and base portions are formed.
 8. A modular seat cushion asdefined in claim 1, wherein: the first and second complementary portionsof the interlocking structure extend substantially over the entire areaof the lower surface and the upper surface of the human interfaceportion and the base portion, respectively.
 9. A modular seat cushion asdefined in claim 1, wherein: the contact configuration extendssubstantially over the entire area of the lower surface of the baseportion.
 10. A modular seat cushion as defined in claim 1, wherein: theseat support structure substantially complements the entire contactconfiguration.
 11. A modular seat cushion as defined in claim 1,wherein: the seat support structure is part of a wheelchair; and theseat support structure is one selected from a group consisting of aplatform seat, sling seat, dropped platform seat, pan seat and seatshell.
 12. A modular seat cushion as defined in claim 1, wherein: thelower and upper surfaces of the human interface and base portions,respectively, are of a substantially complementary shape with oneanother; the interlocking structure comprises the complementary lowerand upper surfaces of the human interface and base portions,respectively.
 13. A modular seat cushion as defined in claim 1, wherein:one of the first or second complementary portions of the interlockingstructure comprises a protrusion extending from the lower or uppersurface of the human interface or base portions, respectively; the otherone of the first or second complementary portions of the interlockingstructure comprises a recess formed into the lower or upper surface ofthe human interface or base portions, respectively; and the recess has acomplementary configuration and size to the configuration and size ofthe protrusion.
 14. A modular seat cushion as defined in claim 13,wherein: the protrusion extends outward from the lower surface of thehuman interface portion; and the recess extends inward from the uppersurface of the base portion.
 15. A modular seat cushion as defined inclaim 14, wherein: the interlocking structure comprises the lowersurface of the human interface portion from which the protrusion extendsand the upper surface of the base portion into which the recess extends.16. A modular seat cushion as defined in claim 14, wherein: a portion ofthe lower surface of the human interface portion adjacent to theprotrusion has a complementary shape to a portion of the upper surfaceof the base portion adjacent to the recess; and the interlockingstructure comprises the portion of the lower surface of the humaninterface portion adjacent to the protrusion and the portion of theupper surface of the base portion adjacent to the recess.
 17. A modularseat cushion as defined in claim 14, wherein: the recess extendscompletely through the base portion to define a hole in the baseportion.
 18. A modular seat cushion as defined in claim 17, wherein: theprotrusion extends through the hole in the base portion and contacts theseat support structure when the human interface and base portions areinterconnected together and the cushion is supported by the seat supportstructure.
 19. A modular seat cushion as defined in claim 1, furthercomprising: a covering that encases the interconnected human interfaceand base portion portions.
 20. A modular seat cushion as defined inclaim 1, wherein: the human interface portion is one of a plurality ofdifferent human interface portions; each different human interfaceportion has a different support contour; the base portion is one of aplurality of different base portions; each different base portion has adifferent contact configuration; and the first complementary portion ofthe interlocking structures of all of the plurality of different humaninterface portions are consistent in configuration with one another; andthe second complementary portion of the interlocking structures of allof the plurality of different base portions are consistent inconfiguration with one another.
 21. A modular seat cushion as defined inclaim 20, wherein: the support contour of one of the plurality ofdifferent human interface portions accommodates the specific anatomy ofthe person.
 22. A modular seat cushion as defined in claim 21, wherein:at least two human interface portions of the plurality of differenthuman interface portions each have a different support contour; and eachof the different support contours accommodates respectively differentgeneralized anatomical proportions of a person within one of at leasttwo different generalized classes of persons.
 23. A modular seat cushionas defined in claim 20, wherein: each of the different support contoursaccommodates respectively different generalized anatomical proportionsof a person within one of at least two different generalized classes ofpersons.
 24. A modular seat cushion as defined in claim 1, wherein: thepredetermined configuration of the seat support structure includes aportion which has essentially the same shape characteristics as thesecond complementary portion of the interlocking structure of the baseportion; and the first complementary portion of the interlockingstructure of the human interface portion interconnects with the portionof the seat support structure which has essentially the same shapecharacteristics as the second complementary portion of the interlockingstructure.
 25. A modular seat cushion as defined in claim 1, wherein:the predetermined configuration of the seat support structure includes aportion which has a shape that is complementary to the firstcomplementary portion of the interlocking structure of the humaninterface portion; and the first complementary portion of theinterlocking structure of the human interface portion interconnects withthe portion of the seat support structure which has a shape that iscomplementary to the first complementary portion of the interlockingstructure.
 26. A modular seat cushion as defined in claim 1, wherein:the seat support structure includes the base portion; and the secondcomplementary portion of the interlocking structure and the contactconfiguration of the base portion are formed in the seat supportstructure as a unitary structure having the shape of the secondcomplementary portion of the interlocking structure.
 27. A modular seatcushion as defined in claim 26, further comprising: a covering thatencases the human interface.
 28. A base structure for attaching a humaninterface portion of a seat cushion to a seat support structure of awheelchair, the human interface portion including a support contour forsupporting an anatomical portion of a person on the cushion, the seatsupport structure having a predetermined configuration for supportingthe seat cushion and the person seated on the cushion, the basestructure comprising: an upper surface having a configuration whichcomplements and interconnects with a portion of the human interfaceportion other than the support contour; and a lower surface having aconfiguration which complements and contacts a portion of thepredetermined configuration of the seat support structure.
 29. A basestructure as defined in claim 28, wherein: the base structure and thehuman interface portion are formed of resilient synthetic plasticsupport material.
 30. A base structure as defined in claim 28, wherein:the seat support structure is one selected from a group consisting of aplatform seat, sling seat, dropped platform seat, pan seat and seatshell.
 31. A base structure as defined in claim 30, wherein: the supportcontour of the human interface portion is one of the plurality ofdifferent support contours each of which accommodates a person ofdifferent anatomical characteristics.
 32. A method of creating a modularseat cushion to support a person from a seat support structure of apredetermined configuration, comprising: selecting a human interfaceportion for the cushion from among a plurality of different humaninterface portions, each different human interface portion having adifferent support contour for supporting a person having differentanatomical characteristics while seated on the cushion; selecting a baseportion for the cushion from among a plurality of different baseportions, each different base portion having a different contactconfiguration which complements at least a portion of the predeterminedconfiguration of a different seat support structure; combining theselected human interface portion with the selected base portion toaccommodate the anatomical characteristics of the person seated on thecushion and the predetermined configuration of the seat supportstructure.
 33. A method as defined in claim 32, further comprising:combining the selected human interface portion with the selected baseportion by interlocking the selected human interface and base portions.34. A method as defined in claim 33, further comprising: interlockingthe selected human interface portion with the selected base portion byinterconnecting complementary portions of the selected human interfaceand base portions.
 35. A method as defined in claim 32, furthercomprising: interconnecting the complementary portions of any of theplurality of different human interface portions with any of thedifferent base portions.
 36. A method as defined in claim 32, whereinthe seat support structure includes a portion having a predeterminedconfiguration which duplicates the complementary portion of the baseportion, and the method further comprises: using the duplicativecomplementary portion of the seat support structure as the base portion;and interconnecting the complementary portions of the selected humaninterface portion and the seat support structure.
 37. A method asdefined in claim 32, wherein the complementary portions of the humaninterface portion and the base portion comprise a protrusion extendingfrom one of the human interface or the base portions and a receptacleextending into the other one of the human interface or base portions,and the method further comprises: interconnecting the protrusion withinthe receptacle.
 38. A method as defined in claim 32, further comprising:preventing the complementary portions from deforming out of theinterconnected relationship when the person is seated on the supportcontour by contacting the contact configuration with the seat supportstructure.
 39. A method as defined in claim 32, further comprising:selecting the human interface portion as one having a support contourwhich specifically accommodates specific anatomical characteristics of asingular person.
 40. A method as defined in claim 39, furthercomprising: selecting the human interface portion as one having asupport contour which generally accommodates the anatomicalcharacteristics of a general class of persons.
 41. A method as definedin claim 32, further comprising: selecting the human interface portionas one having a support contour among a plurality of support contourseach of which generally accommodates the anatomical characteristics of ageneral class of persons.
 42. A method as defined in claim 32, whereinthe seat support structure is part of a wheelchair.
 43. A method asdefined in claim 42, wherein the seat support structure is one of agroup consisting of a platform seat, sling seat, dropped platform seat,and seat shell.
 44. A method as defined in claim 32, further comprising:selecting the human interface and base portions as ones formed ofresilient and breathable synthetic plastic support material.
 45. Amethod as defined in claim 32, further comprising: selecting the humaninterface and base portions as ones formed of resilient syntheticplastic beads which have been fused together.
 46. A method of supportinga person on a cushion in a wheelchair from a seat support structure of apredetermined configuration, comprising: selecting a human interfaceportion for the cushion from among a plurality of different humaninterface portions, each different human interface portion having adifferent support contour for supporting a person having differentanatomical characteristics while seated on the cushion; selecting a baseportion for the cushion from among a plurality of different baseportions, each different base portion having a different contactconfiguration which complements at least a portion of the predeterminedconfiguration of a different seat support structure; combining theselected human interface portion with the selected base portion;positioning the contact configuration of the base portion intocomplementary contact with the predetermined configuration of the seatsupport structure; and seating the person on the support contour withthe anatomical portion of the person in contact with the support contourof the human interface portion while the base portion is incomplementary contact with the predetermined configuration of the seatsupport structure.
 47. A method as defined in claim 46, furthercomprising: maneuvering the wheelchair by action of the user whileseated on the cushion.
 48. A method as defined in claim 47, furthercomprising: removing the person from sitting on the support contour ofthe selected human interface portion; substituting a different selectedhuman interface portion with a different support contour for thepreviously selected human interface portion; combining the selectedsubstituted human interface portion with the selected base portion; andthereafter reseating the person on the support contour of the selectedsubstituted human interface portion with the support contour of thesubstituted human interface portion in contact with the anatomicalportion of the person while the base portion is in complementary contactwith the predetermined configuration of the seat support structure. 49.A method as defined in claim 48, further comprising: maneuvering thewheelchair by action of the user while reseated on the support contourof the selected substituted human interface portion.
 50. A method asdefined in claim 46, further comprising: removing the person fromsitting on the support contour of the selected human interface portion;substituting a different selected human interface portion with adifferent support contour for the previously selected human interfaceportion; combining the selected substituted human interface portion withthe selected base portion; and thereafter reseating the person on thesupport contour of the selected substituted human interface portion withthe support contour of the substituted 10 human interface portion incontact with the anatomical portion of the person while the base portionis in complementary contact with the predetermined configuration of theseat support structure.
 51. A method of attaching a human interfaceportion of a seat cushion to a seat support structure of a wheelchair,the human interface portion including a support contour for supportingan anatomical portion of a person on the seat cushion, the seat supportstructure having a predetermined configuration for supporting the seatcushion and the person seated on the cushion, the method comprising:interposing a base portion between the human interface portion and theseat support structure of the wheelchair; interconnecting the baseportion and the human interface portion; and contacting the base portionin a complementary manner with the predetermined configuration of theseat support structure.
 52. A method as defined in claim 51, wherein thebase structure and the seat cushion are formed of resilient syntheticplastic support material.
 53. A method as defined in claim 51, furthercomprising: selecting the seat support structure from a group consistingof a platform seat, sling seat, dropped platform seat, pan seat and seatshell.
 54. A method as defined in claim 53, further comprising:selecting the support contour of the human interface portion from agroup of human interface portions each of which has a different supportcontours to accommodate different anatomical characteristics.